A sensor apparatus has been proposed that detects acceleration as a physical quantity. For example, a sensor apparatus disclosed in U.S. Pat. No. 6,483,322 corresponding to JP-A-200240047 includes a sensor circuit and a processing circuit. The sensor circuit detects a capacitance varying with acceleration applied thereto and outputs an acceleration signal indicative of the detected capacitance. The processing circuit processes the acceleration signal. The processing circuit has a function to convert the acceleration signal to a voltage signal and to linearly amplify the voltage signal.
When a physical quantity to be detected is small, a sensitivity (i.e., resolution) of a sensor circuit needs to be increased. In such a conventional sensor apparatus, an increase in a sensitivity of the sensor circuit results in a decrease in a dynamic range of the sensor circuit, because an output of the sensing circuit is limited to a power supply voltage. Therefore, if the sensitivity of the sensor circuit is increased to detect a small physical quantity, the sensor apparatus cannot detect a large physical quantity due to a small dynamic range.
One approach to detect a physical quantity at a high sensitivity over a wide range is to use multiple sensor circuits having different dynamic ranges. However, this approach requires multiple sensor circuits and multiple processing circuits for processing outputs of the respective sensor circuits. As a result, the sensor apparatus may be increased in size and cost.